Head positioning suspensions in modern disc drives are designed to be relatively compliant in the normal direction to the disc surface while remaining relatively stiff in all other directions. Compliance in the normal direction (the Z-axis; direction perpendicular to or away from the disc surface) allows the slider to lift off the disc surface and “fly” above the disc while the disc is rotating. Suspension stiffness in all other directions prevents yaw rotation of the head as well as lateral (Y-axis) and linear (X-axis) translation motion while pitch and roll in the head is allowed by the head gimbal assembly.
The head positioning suspension includes a bend section that connects the suspension's base region to the suspension's load beam. The bend section incurs the predominance of the necessary compliance in the form of rotational motion about a transverse or Y-axis that is perpendicular to the suspension's longitudinal or X-axis (the direction of the suspension's extension from the base plate to the slider) and perpendicular to the suspension's out-of-plane or Z-axis. Although rotational compliance about the Y-axis at the bend section is desired, translational motion at the bend section in the Z-axis direction is not advantageous for lowering resonance frequency.
Conventional bend sections are comprised of one or more flat strips of metal spanning the base region to the load beam. Such bend sections have a trade-off between minimizing the Y-axis rotational stiffness and maximizing the Z-axis translational stiffness. Simple beam stiffness relations govern this trade-off. Thus, for a given low Y-rotational stiffness necessary to keep the spring rate low, thus allowing free motion of the slider over the disc surface, there is a limit to how high the Z-axis translation stiffness can be. This trade-off limits other important considerations such as achievable resonant frequencies. In fact, in the case of modem ultra-stiff load beam suspensions, the out-of-plane compliance at the bend section can dominate the resonant response.
Therefore, there is a need for a bend section design that will circumvent the trade-off between low rotational compliance and high translational stiffness inherent in conventional bend section designs.